<!DOCTYPE html>
<html lang="en">
	<head>
		<meta charset="UTF-8">
		<title>Document</title>
		<style>
			* {
				padding: 0;
				margin: 0;
			}

			html {
				/*font-size: 200px;*/
				/*font-size: 6.25em;*/
				font-size: 100px;
			}

			.parent {
				font-size: 0.1rem;
			}

			.child {
				font-size: 1rem;
			}

			.red {
				width: 1rem;
				height: 1rem;
				background-color: red;
			}

		</style>
	</head>
	<body>
		
		<!-- 
			em: 跟父级的字体大小一致
			rem: 跟html的字体大小一致
		 -->
		<div class="parent">
			哈哈
			<div class="child">
				呵呵
			</div>
		</div>

		<div class="red"></div>
		
		
	</body>
</html>




